1. Field of the Invention
The present invention relates in general to a controller for which a capacitor is connected in parallel with an AC machine between the AC machine and a power inverter in order to improve the power factor, thereby increasing an output of the power inverter. More particularly, the invention relates to a controller which is suitable for when the operation of the power inverter is stopped in running and then the power inverter is reactivated to continue the running thereof.
2. Description of the Related Art
FIG. 8 is a block diagram, partly in circuit diagram, showing a configuration of a controller for an AC machine according to the prior art in which a capacitor is connected in parallel with an AC machine between the AC machine and a power inverter in order to improve the power factor. In FIG. 8, reference numeral 1 designates an AC machine; reference numeral 2 designates an AC power supply; reference numeral 3 designates a power rectifier (a diode rectifier or a converter) for converting an alternating current of the AC power supply 2 into a direct current; reference numeral 4 designates a smoothing capacitor for smoothing the direct current into which the alternating current is converted in the power rectifier 3; and reference numeral 5 designates a power inverter (inverter) for converting the direct current into which the alternating current is converted in the power rectifier 3 into an alternating current. In FIG. 8, reference numeral 6 designates a power factor improving capacitor which is connected between the AC machine 1 and the inverter 5 in order to improve the power factor, and reference numeral 7 designates a reactor which is connected in order to prevent a ripple current generated by the inverter 5 from being caused to flow through the capacitor 6. Also, reference numeral 8 designates a controller for manipulating an output voltage of the inverter 5 to control the AC machine 1.
The power factor is improved by adopting the above-mentioned prior art, thereby being able to increase the inverter output. However, in the case where the capacitor is connected, there is the possibility that when the operation of the inverter is stopped, the self-excitation phenomenon may occur between the capacitor and the AC machine depending on the capacitance of the capacitor to generate the over-excitation (overvoltage). In addition, in the prior art, when the overvoltage is generated, the operation state of the system is judged to be abnormal in order to protect the components to stop the system. Thus, there is the possibility that the system is stopped due to the generation of the overvoltage resulting from the connection of the above-mentioned capacitor to reduce the reliability of the system.
In the light of the foregoing, the present invention has been made in order to solve the above-mentioned problems associated with the prior art, and it is therefore an object of the present invention to provide a controller for an AC machine which is capable of even in the case where the overload is generated under the state of connecting a capacitor, reactivating a system without stopping the operation of the system to continue the running.
In order to attain the above-mentioned object, a controller for an AC machine according to the present invention, when reactivating an inverter to continue the running thereof after the operation of the inverter has been stopped, starts the switching of the inverter to reactivate the inverter after a detection value of a DC voltage (Vdc in FIG. 8) of the inverter has been decreased down to the operating value in the running.
According to one aspect of the present invention, there is provided a controller for an AC machine for which a capacitor is connected in parallel with an AC machine between the AC machine and a power inverter in order to improve the power factor, wherein when the operation of the power inverter in running is stopped and then the power inverter is reactivated to continue the running, the reactivation is carried out after a DC voltage detection value of the power inverter has been decreased down to the operating voltage in the running.
According to another aspect of the present invention, there is provided a controller for an AC machine for which a capacitor is connected in parallel with an AC machine between the AC machine and a power inverter in order to improve the power factor, wherein when the operation of the power inverter in running is stopped and then the power inverter is reactivated to continue the running, the reactivation is carried out after a lapse of predetermined time from a time point when a voltage value of the AC machine has been decreased from a rising maximum voltage thereof.
According to still another aspect of the present invention, there is provided a controller for an AC machine for which a capacitor is connected in parallel with an AC machine between the AC machine and a power inverter in order to improve the power factor, wherein when the operation of the power inverter in running is stopped and then the power inverter is reactivated to continue the running, the reactivation is carried out after a voltage value of the AC machine has been decreased down to the normal operating voltage.
According to yet another aspect of the present invention, there is provided a controller for an AC machine for which a capacitor is connected in parallel with an AC machine between the AC machine and a power inverter in order to improve the power factor, wherein when the operation of the power inverter in running is stopped and then the power inverter is reactivated to continue the running, the reactivation is carried out after a lapse of predetermined time from a time point when a velocity detection value of the AC machine has been decreased down to a predetermined value.
According to a further aspect of the present invention, there is provided a controller for an AC machine for which a capacitor is connected in parallel with an AC machine between the AC machine and a power inverter in order to improve the power factor, wherein the operation of the power inverter in running is stopped and then the power inverter is reactivated to continue the running, the reactivation is carried out after a velocity detection value of the AC machine has been decreased down to a predetermined value.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.